Method of forming wound



March 31, 1964 B. G. KUBISIAK 3,126,620

METHOD OF FORMING WOUND MAGNETIC CORES Filed Feb. 4, 1960 Mrlwwy United States Patent M 3,126,620 METHOD OF FORMING WOUND MAGNETEC QORES Bernard G. Kubisiair, Pittsburgh, Pa, assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Feb. 4, was, Ser. No. 6,702 2 Claims. (Ci. 29-15557) This invention relates in general to wound magnetic cores and in particular to a method for forming wound magnetic cores for use in induction apparatus.

Certain types of induction apparatus such as transformers and reactors embody cores comprising wound strips of flexible magnetic electrical steel. In order to improve the magnetic characteristics of these wound cores, a practice has been developed for their manufacture which comprises cutting the strip material forming the wound cores into a number of elements and then repositioning the cut elements through the windows of the induction apparatus electrical windings. The wound core, prior to its assembly into an electrical winding, is generally subjected to a low temperature anneal which results in release of strains set up in the strip material during the winding process. In order to obtain the full advantages of the stress relief anneal, it is essential that the annealed core with its plurality of wound strips is reassembled in the exact sequence and positioning that it was annealed. Thus, unless each curvature of the individual layers in the wound core is repositioned in its exact original location with respect to adjacent curves in other layers, the core will be reassembledin such a manner as to have undesirable stresses. In initially forming the wound core from a strip of electrical steel, the strip is wound substantially tight in order that no sagging occurs in the stress relief anneal. In view of this characteristic of being tightly wound, it is apparent that reassembly of the various subsequently cut strips in the wound core into their exact initial relative positions is not a simple manner. Thus, to facilitate this reassembly step, it is usually desirable to have a slight degree of spacing between the layers of the wound core as it is being formed.

In other methods of manufacturing wound cores, this spacing is provided by inserting shims or spacing elements between the layers prior to annealing. Paper, thread, and other carbon elements have been used as spacing elements. These materials burn or char at the annealing temperatures and the resulting carbon deposits contaminate the annealing ovens. In addition, some of the carbon fragments tend to stick to the core and contaminate the oil surrounding the transformer after it is tanked. Consequently, the annealing ovens must be frequently cleaned. Another method is the formation of raised areas on an antistick coating which is applied to the wound strip in order to prevent the laminations from sticking during annealing. However, this method when applied to the larger sizes of transformer cores can involve a substantial amount of antistick coating material. Depending upon the type of antistick coating material used, the raised spacing areas on the coating also add to the amount of disagreeable carbon residue and dust caused by the coating material burned during the annealing process.

According to this invention, a uniformity of spacing is obtained between the laminations of the wound steel strip by providing deformed raised areas in the surface of the strip prior to winding it into a coil. The strip with the raised areas is then formed into a coil. The raised areas in the wound coil are subsequently flattened, thereby elongating the layers of the coil and providing spacing between them. In such a manner the use of an objectionable spacing material is avoided. Depending upon the type of electrical steel purchased it is also pos- 3,126,620 Patented Mar. 31, 1964 sible to eliminate an annealing step through the practice of this invention. Quite frequently steel is purchased in a semi-finished condition requiring a high temperature annealing treatment prior to use. Where an organic spacer is used it is necessary to subject the steel to this high temperature anneal before spacers are added. This is because the carbon in the organic spacers would migrate into the steel during the high temperature anneal, thereby changing the carbon content of the steel. A low temperature anneal is then performed on the steel after it has been formed into a wound core containing the spacers. This second anneal has been necessary in the prior art in order to relieve stresses set up in the steel during the winding process.

Through this invention which avoids the use of an organic spacer only one anneal is needed when semifinished steel is used. This anneal is a high temperature one and can be accomplished after the core is wound. Thus, the steel is fully finished and stresses from the winding process are relieved in just one annealing step.

It is therefore an object of this invention to provide a new and improved method for forming wound magnetic cores.

A further object of this invention is to provide a wound core having spacing which is formed without the use of additional materials.

Objects and advantages other than those mentioned above will be apparent from the following description;

FIG. 1 illustrates a portion of magnetic strip material having a raised area;

FIG. 2 illustrates a method of flattening the raised areas in a coil of strip material prior to annealing;

FIG. 3 illustrates a second method of flattening the raised areas;

FIG. 4 illustrates a second embodiment of this invention with respect to the method for forming raised areas on the strip material; and

FIG. 5 is a section view of the apparatus illustrated in FIG. 3 taken along line 55.

In accordance with the present invention, magnetic sheet material such as a silicon steel strip 11 is provided with a plurality of raised areas. Each raised area may be formed by a ridge 16 shown in FIG. 1 which has been stamped into the material by a conventional wedge. Although PEG. 1 shows the ridge transversely extending across the entire width of strip 11, the ridges may be made in only a portion of the strips width. FIG. 4 shows another method of providing these raised areas in that a portion of the strip 11 may be cut to cause deflected notched surfaces 17. In the embodiment shown in FIG. 2 the raised areas or ridges 16 have been formed into the strip material at predetermined distances while winding the strip into a circular spiral coil 19 in order that the ridges all appear at substantially one end 21 of the coil in an unaligned pattern. However, the ridges may also be randomly formed in the strip so that they appear throughout the core loop with preferably one or more ridges appearing in each lamination. One ridge in every other layer is also permissible. After the strip material with the ridges is formed into a coil, the ridges are eliminated or substantially reduced to provide space between the layers of the coil.

FIGS. 3 and 5 illustrate one method of removing the ridges or notches. The wound core is placed on a conventional forming mandrel 23 which simultaneously reshapes the loop into a substantially rectangular core and removes the ridges. The circular coil is first placed on adjustable wedge shaped mandrel members 25 and 26. Member 25 is driven to force member 26 outwardly as shown by the arrows, thereby elongating the core. A compressive force is then exerted on three sides of the core by inwardly moving hydraulic rams 27, 28 and 29 espectively. Ram 31 is then forced inwardly and the raised areas or ridges 16 are flattened. The two objectives of reforming the core and removing the ridges are thereby achieved in one operation. Upon flattening the raised areas, which amounts to stamping them back into the plane of their respective laminations, tension between the turns of the loop is reduced, thereby providing space 33 for easy reassembling of the core loop into an electrical coil. Because of the positioning of the ridges at one end of the core and the sequence followed in operating the rams of the mandrel the spaces 33 appear at two corners of the core. Other patterns may be Obtained by randomly stamping ridges into the strip material. In such a case the spacing will appear at the four corners of the core after the core is compressed. The amount of spacing between laminations may be controlled by the size of the ridges.

The method illustrated in FIG. 2 utilizes a pair of rollers 35 which straddle the laminations of the loop and apply a compressive force thereon to remove the ridges. In such a method, the loop is then placed on a reshaping mandrel if the rectangular configuration is desired. After the ridges or notches have been flattened, the wound core is placed into a high temperature stress relief annealer which also fully finishes the grain structure of the steel. Subsequent to the single anneal, the core is then cut into a desired length and reassembled into an electrical coil window.

Thus, it is seen that the invention herein described provides a simple and inexpensive method for forming a wound core with space between adjacent layers which requires no additional shims or other spacing material. Since the stamping of the ridges into the strip can be done automatically as the strip is being formed into a spiral coil, there is no additional time involved.

While only several embodiments of the present invention have been described, it will be apparent to those skilled in the art that additional modifications may be employed without departing from the spirit of the invention or from the scope of the appended claims.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. In a method for making an electrical induction apparatus having a noncircular wound core linked with an electrical winding the steps comprising: providing transverse ridges in the surface of a strip of magnetic sheet material across the entire width of the strip, forming said strip into a coil whereby said ridges are dispersed throughout said coil, substantially flattening said ridges and thus uniformly lengthening said strip to provide spacing between layers of said coil through the sole application of a force limited to compressing the layers together, annealing said coil, cutting said core into a plurality of segments, and reassembling said coil about a leg of said electrical winding.

2. In a method for making an electrical induction apparatus having a noncircular wound core linked with an electrical winding the steps comprising: stamping transverse ridges in the surface of a strip of magnetic sheet material across the entire width of the strip, forming said strip into a coil with a ridge in at least every other layer, applying a compressive force on said ridges to simultaneously flatten said ridges and thus uniformly lengthening said strip for providing spacing between the layers of said coil through the sole application of a force limited to compressing the layers together, and forming said coil into a noncircular configuration, annealing said coil, cutting said core into a plurality of segments, and reassembling said coil about a leg of said electrical winding.

References Cited in the file of this patent UNITED STATES PATENTS 2,305,650 Vienneau Dec. 22, 1942 2,344,006 Steinmayer M 1944 2,387,099 Vienneau Oct. 16, 1945 2,493,414 Morrison Ian. 3, 1950 2,588,173 Somerville Mar. 4, 1952 2,614,158 Sefton et a1. Oct. 14, 1952 2,860,540 Karlsson Nov. 18, 1958 2,907,967 Smith Oct. 6, 1959 3,027,628 Wilk et al. Apr. 3, 1962 FOREIGN PATENTS 658,401 Great Britain Oct. 10, 1951 

1. IN A METHOD FOR MAKING AN ELECTRICAL INDUCTION APPARATUS HAVING A NONCIRCULAR WOUND CORE LINKED WITH AN ELECTRICAL WINDING THE STEPS COMPRISING: PROVIDING TRANSVERSE RIDGES IN THE SURFACE OF A STRIP OF MAGNETIC SHEET MATERIAL ACROSS THE ENTIRE WIDTH OF THE STRIP, FORMING SAID STRIP INTO A COIL WHEREBY SAID RIDGES ARE DISPERSED THROUGHOUT SAID COIL, SUBSTANTIALLY FLATTENING SAID RIDGES AND THUS UNIFORMLY LENGTHENING SAID STRIP TO PROVIDE SPACING BETWEEN LAYERS OF SAID COIL THROUGH THE SOLE APPLICATION OF A FORCE LIMITED TO COMPRESSING THE LAYERS TOGETHER, ANNEALING SAID COIL, CUTTING SAID CORE INTO A PLURALITY OF SEG- 